In recent years much attention has been focused on photocatalytic degradation of organic pollutants by TiO2 particles irradiated by ultraviolet (UV) light. This method is undoubtedly an effective approach toward abatement of a wide variety of harmful/toxic organic pollutants in wastewaters. Unfortunately, the need of an ultraviolet excitation source restricts its technological utility to limited applications. In this work, TiO2/ SiO2 and Pt-TiO2/SiO2 nanoparticles were prepared in anatase form to improve and modify TiO2 photocatalytic activity in UV and visible light. In the case of using SiO2 the results showed that the crystal size and surface area of TiO2 have been improved from17 to 5 (nm) and 80 to 555 (m2/g) respectively. In the case of using platinum (Pt), platinum can be either doped in the crystalline structure of TiO2/SiO2 or deposited on the surface of TiO2/SiO2. The results showed that photocatalytic activity of Pt-TiO2/SiO2 and TiO2/SiO2 has been increased in visible and UV light respectively. The characterizations of catalysts were performed by XRD, FTIR, SEM, TEM, BET and UV-Vis diffuse reflectance spectra. Finally, in order to assess photocatalytic activities of TiO2/SiO2 and Pt-TiO2/SiO2, degradation of monochlorobenzene (MCB) was tested under UV and visible light.